Oximetry is the measurement of the oxygen status of blood. Early detection of low blood oxygen is critical in the medical field, for example in critical care and surgical applications, because an insufficient supply of oxygen can result in brain damage and death in a matter of minutes. Pulse oximetry is a widely accepted noninvasive procedure for measuring the oxygen saturation level of arterial blood, an indicator of oxygen supply. A pulse oximetry system consists of a sensor attached to a patient, a monitor, and a cable connecting the sensor and monitor.
Conventionally, a pulse oximetry sensor has both red and infrared LED emitters and a photodiode detector. The sensor is typically attached to an adult patient's finger or an infant patient's foot. For a finger, the sensor is configured so that the emitters project light through the fingernail and into the blood vessels and capillaries underneath. The photodiode is positioned at the finger tip opposite the fingernail so as to detect the LED emitted light as it emerges from the finger tissues.
The pulse oximetry monitor determines oxygen saturation by computing the differential absorption by arterial blood of the two wavelengths emitted by the sensor. The monitor alternately activates the sensor LED emitters and reads the resulting current generated by the photodiode detector. This current is proportional to the intensity of the detected light. A ratio of detected red and infrared intensities is calculated by the monitor, and an arterial oxygen saturation value is empirically determined based on the ratio obtained. The monitor contains circuitry for controlling the sensor, processing sensor signals and displaying a patient's oxygen saturation, heart rate and plethysmographic waveform. A pulse oximetry monitor is described in U.S. Pat. No. 5,632,272 assigned to the assignee of the present invention.
The patient cable provides conductors between a first connector at one end, which mates to the sensor, and a second connector at the other end which mates to the monitor. The conductors relay the drive currents from the monitor to the sensor emitters and the photodiode detector signals from the sensor to the monitor.